1. Field of the Invention
This invention relates to a size for textile fibers. More particularly, the invention relates to a novel size for textile fibers which comprises a modified polyvinyl alcohol type resin obtainable by the alkali saponification of a copolymer comprising a vinyl ester, typically vinyl acetate, and an ethylenically unsaturated dicarboxylic acid substantially free from the monoester, diester and anhydride as essential and predominant copolymeric units, which size has excellent adhesive and cohesive affinities for textile fibers as well as improved desizing properties and workability.
2. Description of the Prior Art
Whereas starch, polyvinyl alcohol, acrylic copolymers, etc. are conventional textile sizes, those sizes have their own disadvantages and cannot be used alone successfully with different kinds of textile fibers. This has compelled one to use two or more of such sizes in various formulations. The problems encountered when two or more different sizes are used in combination include the instability of the resultant composition size due to the poor compatibility of component sizes, the poor desizing efficiency arising from the dissimilar optimum desizing conditions for component sizes, the complexity of treatment of desizing effluents, etc. Recently, in particular, the disposal of waste water has become an important consideration from the standpoint of environmental protection.
The continued use of mixed sizes notwithstanding the above problems is because no single known size is able to discharge the multiple functions required of sizes for textile fibers. The characteristics of the representative commercial textile sizes heretofore in use are set forth in the following table.
______________________________________ Polyvinyl Acrylate Characteristics Starch alcohol size ______________________________________ (1) Cost .circleincircle. O x (2) Properties of x .circleincircle. O size film (3) Adhesion to x x O synthetic fiber (4) Stripping of size x O O on weaving (5) Gumming up tendency O O x (6) Odor of size solution O O x (7) Stability of size x O O solution (8) Treatment of desiz- O O x ing effluent ______________________________________ .circleincircle. Very desirable, O Desirable, X Undesirable
It will be apparent that while starch is the oldest, commonest and least expensive size of all, it ranks very low in functional terms, for it gives only a harsh and brittle film. Often called "synthetic starch," polyvinyl alcohol is a water-soluble synthetic high molecular weight substance containing a large number of hydroxyl radicals just as does starch. Because it yields a considerably tougher film than starch, with excellent cohesive and protective properties with respect to fiber, polyvinyl alcohol has rapidly come into use, replacing starch, as a textile size over the past decade or so.
Nonetheless, polyvinyl alcohol sizes have one disadvantage; i.e. an inadequate "bonding" or adhesive affinity for synthetic fiber. The acrylate size, on the other hand, has a property compensating for the above disadvantage of polyvinyl alcohol, that is an excellent adhesive affinity for synthetic fiber. However, this size is not only expensive but, because of the several disadvantages mentioned above, is rarely employed alone. Thus, acrylate size has been added as a modifier to starch or polyvinyl alcohol sizes for the purpose of increasing their adhesive affinity for synthetic fiber. Furthermore, both starch and polyvinyl alcohol are able to be microbiologically degraded and, as such, lend themselves well to the treatment of desizing effluents. In the case of acrylate sizes, no suitable strain of microorganism has been discovered that would degrade them and, therefore, in consideration of effluent disposal, it is preferable not to add an acrylate size.
In view of the current status of textile sizes, it was thought that if it were possible to overcome the disadvantage of polyvinyl alcohol size, i.e. its low adhesive affinity for synthetic fiber, so that the size could be utilized without the addition of an acrylate size, a considerable commercial advance could be materialized. From the above point of view, several proposals have been made as to the improvement of sizing characteristics by the modification of polyvinyl alcohol by way of copolymerization.
By way of illustration, it is stated in Japanese Patent Publication No. 5978/1964 that a textile size based on a resin which is obtainable by partial or complete saponification of the vinyl acetate units in the copolymer of vinyl acetate with at least a comonomer selected from the group consisting of unsaturated aliphatic dicarboxylic acid dialkyl esters, acrylic acid alkyl esters and vinyl alkyl ethers and at least a member selected from the group consisting of unsaturated aliphatic dicarboxylic acid monoalkyl esters has superior properties.
It is disclosed in Japanese Patent Publication No. 7060/1968 that a saponification product of a crotonic acid-olefin-vinyl acetate copolymer is a suitable size for hydrophobic fibers.
Japanese Patent Application Laid-open No. 66988/1974 states that a partial saponification product of a maleic acid monoalkyl ester-vinyl acetate copolymer within a certain range is a size suitable for hydrophobic fibers.
Japanese Patent Publication No. 32355/1975 discloses a textile size based on a modified polyvinyl alcohol containing 0.1 to 15 mole percent of lactone rings within its molecule and teaches a method for producing the same which comprises saponifying an unsaturated carboxylic acid ester-vinyl acetate copolymer and neutralizing the saponified copolymer partially with an acid.
U.S. Pat. No. 3,689,469 teaches that a saponified vinyl acetate-methyl methacrylate copolymer having a specified composition and essentially "free from acid" in its molecule is a suitable size for textile fibers and shows that the presence in the copolymer of acid leads to deteriorations in desizing properties. This specification further includes a description suggesting that, in the saponified copolymer, all the carboxyl groups derived from the methyl methacrylate units form intra-molecular esters lactones with the hydroxyl groups of the adjacent vinyl alcohol units.
The adhesive affinities for synthetic fibers of the polyvinyl alcohol type resin prepared by the copolymerization and modification with an unsaturated carboxylic acid alkyl ester or crotonic acid and an olefin or the like are still inadequate and are useful only in limited applications when used alone. Thus, in many general applications, such resins cannot discharge the functions required of a textile size as far as they are singly employed, it being thus still essential to enlist the help of an acrylate size component.